1. Field of the Invention
The present invention relates to a power source control unit of an electric supercharger to suppress effects on on-vehicle electrical equipments by operation of an electric supercharger that is disposed in an intake passage of an internal combustion engine and driven by an electric motor and, in particular, to a power source control unit of an electric supercharger using a generator and two batteries in combination.
2. Description of the Related Art
Recently, superchargers acting to increase an intake pressure of an internal combustion engine using exhaust energy to augment its output have been widely utilized.
Incidentally, the term “supercharger” includes an apparatus to supply air for combustion into a cylinder of an internal combustion engine with higher pressure than is obtained from natural intake.
Furthermore, electric superchargers have been developed to be mounted on the mentioned supercharger for the purpose of raising transient response as well as improving fuel consumption of automobiles, and the electric superchargers are to cover the shortage of supercharge of the supercharger at the time of low engine speed.
Since, however, a large torque is required at the time of driving an electric supercharger, a large electric current flows to the electric supercharger. Therefore, any voltage drop or voltage fluctuation occurs at a battery terminal and there is a possibility to adversely affect on-vehicle electrical equipments.
For example, in “Control Unit of Turbocharger equipped with Electric Rotating Machine” described in the Japanese Patent Publication (unexamined) No. 98987/1993, a battery is used for power supply of an electric supercharger, and a generator is used for power supply of on-vehicle electrical equipments.
On the occasion of charging the battery, a surplus of exhaust energy is converted to an electric energy using the electric supercharger to charge the battery to a predetermined battery charge amount. Thereafter, charging the on-vehicle electrical equipments is conducted using the generator. In this manner, adverse effects on the on-vehicle electrical equipments owing to voltage drop are suppressed.
For another example, in “Power Source Unit of Vehicles” described in the Japanese Patent Publication (unexamined) No. 346747/1994, a battery and a capacitor are employed as the power supply source of an electric supercharger, and in which the capacitor is used in the beginning of driving the electric supercharger that needs a large electric current, and thereafter the electric supercharger is driven by the additional use of the battery.
Further, when power generation is conducted by the electric supercharger using a surplus of exhaust energy, a capacitor having superior charge or discharge characteristics is charged, and after its full charge has been done, the battery is charged. In this manner, an efficient charge or discharge can be conducted.
In the above-mentioned Japanese Patent Publication (unexamined) No. 98987/1993, at the time of driving the electric supercharger, power supply to the on-vehicle electrical equipments is conducted using the generator.
There is, however, a possibility that a sufficient amount of electric power the on-vehicle electrical equipments will need cannot be supplied only by the generator. Moreover, in case of more power generation of the generator, the engine load is increased and fuel consumption will come worse.
In the above-mentioned Japanese Patent Publication (unexamined) No. 346747/1994, in the case that the electric supercharger is driven to be on or off, the power supply from the capacitor cannot be conducted and there is a possibility that the voltage fluctuation of the battery occurs due to that the electric supercharger is driven.